In recent years there has been a tremendous amount of interest in transparent armor for both military and civilian protection. It is desired that the transparent armor is abrasion resistant, relatively low cost, and relatively low weight, and in many applications, it is desired that the transparent armor is optically clear. Likewise since there are countless types of threats (bullets, improvised explosive devices (IEDs), etc.), transparent armor preferably should be effective against multiple types of projectiles and preferably against multiple strikes.
In many instances, transparent armor constructions consist of a hard ceramic layer, which may be bonded to a polymeric layer. The hard ceramic layer is abrasion resistant and resists scratches during normal use. When a projectile encounters the transparent armor, the hard ceramic layer deforms the projectile and resists penetration by the projectile while the polymeric layer supports the ceramic layer and further absorbs energy from the projectile. The combination of the hard ceramic and polymeric layers causes disintegration of the projectile and inhibits the penetration of the projectile through and possibly cause injury. The selection of the particular ceramic layer, and polymeric layer, depends upon the desired end properties of the transparent armor.
One particular transparent armor material is a polycrystalline magnesium-aluminate spinel ceramic (e.g., MgAl2O4). This material is typically hot-pressed to form the shape, and to produce a dense, pore-free ceramic body. Due to contact with the hot-press platen surfaces, the resulting outer surfaces of the ceramic have a textured, orange-peel-type surface. Even if the hot-pressed ceramic body is dense and pore-free, the rough outer surfaces cause scattering of incident light and thereby result in a non-transparent product. In order to obtain a transparent product, both surfaces must be polished smooth.
However, it is time consuming and difficult to polish the hot-pressed material to optical clarity. The polishing cost may contribute significantly to the overall transparent armor cost and thus inhibit their use.
What is desired is a cost effective means to polish a transparent armor material to achieve optical clarity.